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This manuscript describes the syntheses, structures and magnetism of Mn III -Ca II /Sr II complexes which are compositionally relevant in the context of the oxygen evolving complex (OEC) of photosystem II (PS II). A series of trimetallic tetraoxo complexes containing redox-inactive metal ions Ca II or Sr II were synthesized using a tetranucleating ligand framework. The structural characteristics of these complexes, with the oxido ligands bridging the redox-inactive metals and the manganese centres, make them particularly relevant to biological and heterogeneous metal-oxido clusters. Electrochemical studies of these compounds show that the reduction potentials are highly dependent upon the Lewis acidity of the redox-inactive metal, identifying the chemical basis for the observed differences in electrochemistry. This correlation provides insights into the role of the Ca II /Sr II ion in modulating the redox potential of the OEC and of other redox-inactive ions in tuning the redox potentials of other metal-oxide electrocatalysts. Temperature dependent magnetic measurements have also been performed for the complexes.

We report the first example of a covalently bound dimer of monolayer protected atomically precise silver nanocluster [Ag25(DMBT)18]- (DMBT stands for 2,4-dimethylbenzenethiol). Covalently linked dimers could be important to design new cluster assembled materials with composite properties.

In this work, we have strategically incorporated a quinoxaline derivative and a diaminomaleonitrile moiety to construct a chemosensor, 2-amino-3-[(quinoxalin-2-ylmethylene)-amino]-but-2-enedinitrile (H2qm). The notable feature of this strategy is to generate a highly conjugated Schiff base platform with interesting binding properties. Remarkably, H2qm exhibited a visual sensing ability towards Cu2+ in 100% aqueous medium. The effectiveness of the chemosensor has been demonstrated by utilizing it to determine the Cu2+ concentration in real samples. Interestingly, the reaction between H2qm and Cu(ClO4)2·6H2O in DMSO yielded a quinoxaline-2-carboxylic acid based compound and single crystal X-ray diffraction analysis unveiled the resulting structure as [(qa)2Cu(H2O)2] (Hqa = quinoxaline-2-carboxylic acid).

An efficient Rh-catalyzed oxidative C-H activation/annulation of 2-arylquinoxalines with internal alkynes is described using Cu(OAc)2·H2O and AgBF4 to afford a diverse variety of substituted quarternary ammonium salts at room temperature. The mechanism of the protocol is established on the basis of isolation of the 5-membered rhodacycle intermediate and kinetic isotope studies. The mild reaction conditions, substrate scope and functional group diversity are the salient practical features.

A facile and reliable method to monitor strongly acidic pH was developed. The sensing mechanism was found to involve the protonation-deprotonation equilibrium of the synthesized probe HQphy (1) (N-phenyl-N'-quinoxalin-2-ylmethylene-hydrazine) within a working range of pH 0.7-2.7. The eventual sensing of Fe3+ was the outcome of acidity imparted by [Fe(H2O)6]3+ ions in solution during the formation of [Fe(H2O)5(OH)]2+. The protonation-deprotonation phenomenon of HQphy was investigated using 1H NMR and single crystal X-ray diffraction experiments. The protonated probe, H2Qphy+, was crystallized with FeCl4-/ClO4- counter anions as [H2Qphy][FeCl4]·H2O (2)/[H2Qphy][ClO4]·H2O (3). A further complex containing the [H2Qphy] cation (4) was also formed. The complexes were characterized by SC-XRD experiments. Moreover, single crystal to single crystal transformation is observed between 1 and 3. In order to understand the sensing mechanism, various analytical studies, such as UV-Vis titration, ESI-MS spectrometry analysis and 1H NMR, were carried out in detail. A theoretical study correlates well with the experimental data, where the π(L) → π*(L) transition of the ligand is red shifted by 100 nm due to protonation of the quinoxaline moiety. The probe enables discrimination of trihalo acetic acid from its mono- and di-analogues.

Iron-catalyzed dioxygenation of alkenes in air using N-hydroxyphthalimide (NHPI) and N-hydroxybenzotriazole (HOBt) is described at room temperature. The products can be readily converted into 1,2-vicinal diols using PPh3 and Mo(CO)6. The use of Fe(NO3)3·9H2O as the catalyst, mild reaction conditions and the selectivity are the significant practical features. The radical scavenger experiment suggests that the reaction proceeds via a radical intermediate. The synthetic and mechanistic aspects have been presented.

The β-turn conformation and FRET process were established in the designed tripeptide containing fluorescent triazolyl donor and acceptor-decorated unnatural amino acids separated by a natural alanine.